Electric discharge device



Nov. 18,1947.

J. GJW. MULDER ELECTRIC DISCHARGE DEVICE Filed Jan. 25, 1945 2 Sheets-Sheet l 32212122 0? f v GMZ Muldef.

fly flau% Attorney Nov. 18, 1947. J. Ye. W. MULDER ELECTRIC DISCHARGE DEVICE Filed Jan. 25, 1943 2 sheets sheet 2 zhvera or G. WMalder'.

flflbrrwy Patented Nov. 18, 1947 UNITED STATES PATENT OFFICE hoven,

Netherlands, assignor to Hartford National Bank and Trust Company, Hartford,

Conn., as trustee Application January 23, 1943, Serial No. 473,404 In the Netherlands December 2, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires December 2, 1960 4 Claims.

This invention relates to a current-converting disc e tube comprising an incandescent cathode, one or more anodes and one or more screens, which are arranged intermediate the cathode and the anodes.

Tubes of this kind are provided with a gas and/or vapour-filling for neutralizing the space charge at the cathode. The maximum operatin pressure of the filling is limited b the requirement that back-discharges at the maximum negative anode voltage prevailing in the non-conducting phase are to be avoided. The minimum operating pressure of the filling is limited by the fact that the life of the cathode greatly decreases at a low pressure inter alia due to the considerable increase of the cathode-disintegration.

It has been therefore necessary so to influence the discharge path between the cathode and the anode either by the use of anode arms or by the use of screens, in order to attain the desired blocking voltage at a pressure ensuring a satisfactory life of the cathode. However, the use of such anode arms or screens resulted not only in a certain increase of the starting-up voltage in either direction but also in a falling-off in the constancy and/or reproduction of the startin up voltage in the pass-direction. In a number of cases the latter difficulty is the most important. A certain increase of the starting-up voltage in the pass-direction has little influence on the output to be obtained, particularly with high voltages to be rectified, but the influence of irregularities in the value of the starting-up voltage may frequently be a source of much trouble. In some instances it has been suggested to eliminate or reduce these disadvantages by means of auxiliary ionisation. This, however, involved certain complications in the construction of the discharge tube and the circuit arrangement such, for example, as auxiliary anodes in the discharge path with the associated supply sources or potentiometers.

The invention has for its object to ensur the low, constant and reproducible starting-up voltage in the pass-direction in a quite simple manner in the case of the above-mentioned increase in blocking capacity. This obviates the need for the above-mentioned circuit arrangements and electrode for auxiliary ionisation unless still higher uniformity and reproduction are to be obtained by combination of the measure of the invention with the said means, in which case an even lower starting-up voltage in the pass-direction is realized.

According to the invention the discharge tube comprises a screen interposed between the cathode and the anodes which screen provides for a curved main discharge path between the cathode and anode and is provided with one or more apertures producing an auxiliary discharge path and through which electrons emitted by the cathode may reach the immediate proximity of the anodes even prior to the ionization of the main discharge path. The apertures are so positioned relative to the cathode and anodes that the probabilit of coarse particles such as particles of emitted material driven from the cathode impinging on the anodes is practically zero. Furthermore, the apertures have an area which is small with respect to the area of the main discharge path, said area being presumably less than 5% of the area of the main discharge path.

By means of the above construction the abovementioned starting-up ditficulties are avoided. More particularly, the ionization required for initiating the main discharge may readily take place by reason of the fact that such ionization is not forced to follow the path of the main discharge which path is relatively long and frequently along charged surfaces. Furthermore, the construction obviates the possibility that particles from the emitting cathode may deposit on the anodes. A further advantage is that the expedient is extremely simple and cheap.

The object of the invention may be attained by so arranging the apertures that a straight line drawn from any portion of the active surface of the cathode through the auxiliary apertures only pass closely past the anode without such a line intersecting its active surface. It has been found that electrons from the electron cloud around the cathode are accelerated to a suificient extent to ionize the surroundings of the anode, whereas, due to their larger mass, the coarser material particles received from the cathode are deflected from their original path to a considerably lesser extent only and hence cannot reach the active surface of the anode.

On the other hand there are current-converting tubes in which the cathode already operates under comparatively favourable conditions so that material particles detached from the cathode are hurled away at comparatively long intervals only. In this case, in divergence from the geometrical criterion put forward hereinbefore, it is possible so to arrange the auxiliary apertures that straight lines may be drawn from the active surface of the cathode through the auxiliary apertures which strike the active suriace of the anode. In view thereof auxiliary apertures in the screen are given such small dimensions that the probability that a cathode particle may find its way to the anode through the apertures is practically zero, the effect of the invention in respect of the starting-up voltage in the pass-direction being nevertheless obtained.

For this purpose it is preferable that the auxiliary apertures should have such dimensions that.

the largest solid angle from any point of the active surface of the cathode through the apertures is less than 0.6 of a degree. In this case we may refer to a static criterion in contradistinction to the geometrical criterion given above. Assuming, for example, the probability that due to sputtering of the cathode an operation-disturbing material particle is hurled into space from the cathode, without a cathode screen being provided, to be low per se, for example once in a month. Such behavior is by itself suiiicient to characterise the tube concerned as insuificiently reliable in its action. In such a case it is sufficient to provide a screen having an auxiliary aperture in the direction of the anode of such size as to reduce the probability of such action to about With such an aperture screen the anode may be expected toreceive cathode material once in nearly two years so that the tube can be considered fully satisfactory from the viewpoint of reliability and at the same time satisfactory starting characteristics are obtained.

If a cylindrical helical incandescent cathode is supported at the ends the probability of service-disturbing sputtering at the ends is a max- Fig. 1 is a part-sectional front elevation of a rectifier valve comprising a discharge vessel I, an incandescent cathode 2 and anodes 3. The diameter of the discharge vessel is 100 mm. so that the other dimensions of the tube can be readily derived therefrom Connection to the cathode 2 is made by means of pole wires 4 screened by small ceramic tubes 5, and by means of small sealing-in hoods 6 provided with connecting strips 1. The anodes 3 are mounted on pole wires 8 which, protected by small ceramic tubes 9, are taken through the top of the tube by means of small sealing-in hoods l0 and which end in wire studs ll. The independent anodes are surrounded by cylindrical screens I2 of wire gauze which only leave free the front surface of the anode, the anodes being separated by a plate-shaped screen It which extends in the direction of the cathode 2 beyond the front surfaces of the anode 3 and is intended to avoid the occurrence of flashing-over between the anodes. The axes of the anodes and of the pole-wires of the cathode are arranged symmetrically and lie parallel to the axis of the cylindrical discharge vessel, the cathode being arranged across this axis. On the small tubes 5 is mounted a metal imum because, due to the dissipation of heat along the supporting members, the ends may assume a lower temperature than the centre. The ions from the main arc discharge, however, have a tendency to even distribution over the cathode surface and this results in increased bombardment by ions and hence in sputtering at the ends, particularly during the heating-up period of the cathode. Thus, it is preferable to separate such a cathode from the anode by a screen in which the auxiliary apertures are located substantially midway between the supporting points of the cathode. The probability of disturbances by back-discharge is considerably decreased by the use of this measure.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawings in which Figure l is a front elevation partly in crosssection, showing a two-anode rectifier valve in {accordance with one embodiment of the invenion.

Figure 2 is a section taken along the line II-II of Figure 1.

Figure 3 is a front elevation partly in crosssection showing a two-anode rectifier valve in accordance with another embodiment of the invention.

Figure 4 is a side elevation partly in crosssection of the valve of Figure 3.

Figure 5 is a front elevation partly in crosssection showing a single-anode rectifier valve in accordancewith the embodiment of the invention shown in Figures 1 and 2.

Figure 6 is a partial side elevation of the oath? ode-anode system of the tube of Figure .5. i

The tubes shown in Figs. 1, 2 and 5, 6 illustrate the arrangement of auxiliary apertures accords ing to the geometrical criterion, whereas the tube shown in Figs. 3, 4 illustrates such arrange: ment according to the static criterion,

iii!

cylindrical screen M which jointly with a bottom plate l5 and a covering plate l6 surrounds the cathode on all sides and intermediate the cyl inder I l and the covering plate i6 is recessed an annular slot I! for the passage of the main discharge, whose free section is about 10.4 square centimetres. The covering plate i6 is provided with four circular auxiliary apertures l8 having a diameter of mm. As is clearly seen in Fig. 1, the apertures are arranged in such manner that straight lines drawn from the cathode through the apertures do not intercept the active surface of the anodes 3. The auxiliary apertures consequently comply with the geometrical criterion above discussed. The apertures'have a total area of 0.28 cm.'', i. e., 2.7% of the free section of the pass aperture for the main discharge. The screen I4 is connected to a wire stud 19 so that a potential may be applied to it. The tube is intended for a maximum efiective anode alternating voltage of 2x125 volts and a maximum blocking voltage of 270 volts, at a maximum average rectified current of 30 amperes. The tube is filled with argon at less than 1 mm. mercury pressure and with saturated mercury vapour which is received from a mercury supply 29 housed in a metal cap 22 which is arranged at the coldest point of the tube and is cooled by means of a metal strip 23 so that the condensation temperature of the mercury cannot greatly exceed the room temperature.

Figures 3 and 4 are part sectional front-elevations of an incandescent cathode rectifier valve according to the invention in which two anodes are contained. The discharge vessel 25 (about mm. in diameter) contains a cathode 26 and two anodes 21 mounted in a similar manner to that of the first example. The anodes are sep arated by a plate-shaped screen 28 carrying a prismatic metal cathode screen 29 which is open at the bottom. The two faces of the sleeve adjacent to the anodes are each provided with an auxiliary aperture 38 which is 2 millimeters in diameter. In the arrangement of Figs. 3 and 4 straight lines can be drawn between the active surfaces of the cathode and one of the anodes through the said apertures and the embodiment accordingly complies with the static criterion above discussed. This tube also has a gas and vapour filling as indicated hereinbefore in respect of the tubes of Figs. 1 and 2.

Fig. 5 is a part-sectional front view of an incandescent cathode rectifier valve and Fig. 6 is a side view of part of the electrode arrangement of this tube. The discharge vessel El 110 mm. in diameter contains an incandescent cathode 32 and an anode 33 which are taken out at the bottom and the top respectively of the discharge vessel by means of ferrochrome seals 35 and 34 respectively. The pole wires 35 and 31' of the incandescent cathode 32 carry, on one side of the intermediary of a small ceramic tube 38, a bridge piece 39 upon which is supported a cathode screen 40 in which an aperture ti about 2 mm. in diameter is formed. Fig. 6 clearly shows that the cathode 32, the anode 33 and the aperture 4| are so arranged relatively to each other that straight lines drawn from the active surface of the cathode only pass past the anode so as almost to touch it but do not reach it in any case. Again, the tube shown in Fig. 5 is provided with an argon filling at 0.17 mm. pressure and a saturated mercury vapour filling. The maximum admissible anode alternating voltage has a R. M. S. value of 85 volts, the maximum average rectified current is amperes, whereas the maximum blocking voltage has a top value of 240 volts. The starting-up voltage in the pass-direction may be reduced by the measure according to the invention from an amount varying between 17 and 28 volts to the reproducible amount of 16 volts.

What I claim is:

1. An electric discharge tube comprising a container, an ionizable medium, an incandescent cathode and an anode spaced apart within the container, and means to produce between the cathode and the anode a curved main discharge path and a substantially straight auxiliary discharge path for facilitating ionization of said medium, said means comprising a shielding mem ber interposed between the cathode and anode and provided with an aperture so dimensioned that the cross-sectional area of the auxiliary discharge path through the aperture is substantially smaller than the cross-sectional area of the main discharge space, said aperture having dimensions and position as to substantially prevent cathode material from impinging on the anode.

2. An electric discharge tube comprising a container, an ionizable medium, an incandescent cathode and an anode spaced apart within the container, and means to produce between the cathode and the anode a curved main discharge path and a substantially straight auxiliary discharge path for facilitating ionization of said medium, said means comprising a shielding member interposed between the cathode and the anode and provided with an aperture, said aperture being so dimensioned that the cross-sectional area of the auxiliary path is substantially smaller than the cross-sectional area of the main discharge path and being so arranged that a straight line from any active portion of the cathode through the aperture passes adjacent to the anode without intercepting the active surface thereof.

3. An electric discharge tube comprising a container, an ionizable medium, an incandescent cathode and an anode spaced apart within the container, and means to produce between the cathode and the anode a curved main discharge path and a substantially straight auxiliary discharge path for facilitating ionization of said medium, said means comprising a shielding member interposed between the cathode and the anode and provided with an aperture, said aperture being so dimensioned that the cross-sectional area of the auxiliary path is substantially smaller than the cross-sectional area of the main discharge path and that the maximum solid angle subtended by the aperture from any active portionof the cathode to the active surface of the anode is less than about 0.6 degrees.

l. An electric discharge tube comprising a container, an ionizable medium, a cylindrical-helical incandescent cathode and an anode spaced apart within the container, and means to produce between the cathode and the anode a curved main discharge path and a substantially straight auxiliary discharge path for facilitating ionization of said medium, said means comprising a shielding member interposed between the cathode and anode and provided with an aperture, said aperture being so dimensioned that the cross-sectional area of the auxiliary path is substantially smaller than the cross-sectional area of the main discharge path and that the maximum solid angle subtended by the aperture from any active portion of the cathode to the active surface of the anode is less than about 0.6 degrees and being arranged to expose the hottest portion of the cathode to the anode.

J OHANNES GIJSBERTUS WILHELM MULDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,107,945 Hull Feb. 8, 1938 2,084,725 Dallenbach June 22, 1937 2,217,185 Smith Oct. 8, 1940 FOREIGN PATENTS Number Country Date 377,041 Great Britain July 21, 1932 

